Conventionally, there have been known various types of substrate processing systems configured to perform a process such as a liquid process by a processing liquid, a gas process by a processing gas, a cleaning process or a heating process on a substrate such as a semiconductor wafer. A substrate processing system includes a substrate mounting table configured to mount thereon a substrate receptacle which accommodates therein a multiple number of substrates; and a multiple number of substrate processing units which have the same structure and are arranged in multiple levels. Each substrate processing unit includes a multiple number of substrate processing modules configured to perform various processes on a substrate. Further, a substrate buffer configured to temporarily accommodate therein a multiple number of substrates is also provided in each substrate processing unit. Substrates are taken out of the substrate receptacle on the substrate mounting table by a first substrate transfer device and transferred into the substrate buffers of the respective substrate processing units. Then, the substrates in each substrate buffer are transferred into the respective substrate processing modules of the substrate processing units by a second substrate transfer device. Then, the substrates processed in the substrate processing modules of the substrate processing unit are returned back into the corresponding substrate buffer by the second substrate transfer device.
Patent Document 1: Japanese Patent Laid-open Publication No. 2003-273058
As stated above, each substrate processing unit includes the multiple number of substrate processing modules and the second substrate transfer device configured to transfer a substrate between the substrate processing modules and the substrate buffer. When abnormality occurs, for example, when the second substrate transfer device within any one substrate processing unit is broken down, a substrate to be processed by this substrate processing unit may be left unprocessed in the substrate buffer of the substrate processing unit for a long time until the second substrate transfer device is properly repaired.
As stated, if abnormality occurs in any one substrate processing unit, an unprocessed substrate, if any, may be left in the substrate buffer of that substrate processing unit for a long time.